The United States expressed concern to "high level" officials in Beijing after Chinese police reportedly detained and beat up two sons of exiled Uighur leader Rebiya Kadeer in the second move against her family this week.

The duo were taken into police custody together with seven other family members in China's predominantly Muslim Xinjiang region, according to Kadeer's daughter Akida Rouzi.

"One of my brothers has been taken to hospital and we don't know the condition of the other," said a sobbing Rouzi, reached by telephone in Washington.

They were "beaten half to death" in Nansan, a camping site in Urumqi, she said. "We are worried and helpless, everyone is crying. I really wish there was more we could do."

The State Department said in a statement Thursday that it was "deeply concerned" by the reported detention of Kadeer's three adult children and that "one or more may have been beaten."

Washington has "raised our concerns with high-level Chinese government officials and have strongly urged them to investigate these reports and to release Ms. Kadeers children, if they are under any form of detention," the department said in a statement.

"We will continue to urge that they be allowed to move and act freely."

In addition, the department said, "we are continuing to seek information on the welfare and whereabouts of Ms. Kadeer's children and are working to contact them directly."

Policemen had herded Kadeer's sons, Ablikim, 32, and Alim Abdiriyim, 30, her daughter, Rushangul, 36, and their spouses and children into a truck and took them to the camping site where the beatings took place, Rouzi said.

"While they were beating up my brothers, my sister called me up using a cell phone before the conversation was cut off," she said.

Ablikim, Alim and Rushangul were first thrown into a police lock-up on Monday and placed under house arrest the next day under heavily armed police guard.

"The Chinese police have beaten my sons and terrorized my grandchildren," Kadeer said Thursday. "This is just the most diabolical treatment of my family -- this is what we, the Uighur people, are up against," she said.

The 60-year-old mother of 11 was a millionaire businesswoman and a high-profile Uighur political prisoner who became a symbol of the struggle of her eight-million-strong community.

She was deported to the United States following her release in March last year from six years of detention in Beijing.

Amnesty International said the alleged intimidation of Kadeer's family smacks of "blackmail" by the Chinese authorities.

"This is a blackmail, holding children as hostages to silence Rebiya Kadeer in her attempt to bring democracy and restore human rights in Xinjiang," said T. Kumar, Amnesty's Washington-based Asia Pacific advocacy director.

Uighur Muslims, who maintain a distinct ethnic identity from the Chinese, are seeking their own homeland on territory that is now part of northwestern China.

They have been struggling to re-establish the independent state of East Turkistan in Xinjiang since the province became an autonomous region of China in 1955.